1. Field of the Invention
The present invention relates to a method of automatically detecting the amount of remaining sheets of paper in a paper feeding cassette of a printing apparatus.
2. Description of the Related Art
For instance, a cassette 20 containing a plurality of sheets of paper S is detachably installed in a printing apparatus such as a printer or copier, as shown in FIG. 1. A pickup roller 11 closely contacting the uppermost surface of the stack of paper S in the cassette 10 when the cassette 20 is coupled to a main body 10 of the printing apparatus so that the stack of paper S is provided one by one through a paper feeding path according to rotation of the pickup roller 11.
However, in the conventional printing apparatus, when the stack of paper S, in the cassette 20, is gradually consumed during a printing job, a user cannot see how many sheets of paper S are left in the cassette 20 unless the cassette 20 is drawn out of the main body 10. Thus, there frequently are cases in which the printing job is stopped due to lack of paper. Additionally, it is inconvenient to check the amount of paper remaining prior to a printing job by drawing the cassette 20 out, thereby preventing the above problem. Therefore, there exists a need for a method of detecting the amount of paper remaining in the cassette 20, without drawing the cassette 20 out of the main body 10.
To solve the above problem, it is an objective of the present invention to provide a method of detecting the amount of remaining sheets of paper in a cassette, without drawing the cassette out of the main body of a printing apparatus.
Accordingly, to achieve the above objective, there is provided a method of detecting the amount of remaining sheets of paper in a paper feeding cassette of a printing apparatus, wherein the printing apparatus receives a paper feeding cassette having a knock-up plate on which paper is placed, and which pivots as paper is removed therefrom, a pickup roller installed in the printing apparatus which elastically moves up and down within a predetermined range to contact the paper, the pickup roller being made to rotate in close contact with the paper to sequentially feed the paper into the printing apparatus, a lifting mechanism which lifts the knock-up plate step by step according to the consumption of paper, thereby placing the loaded paper against the pickup-roller, calculating a difference in the number of operations of the lifting mechanism for lifting the knock-up plate toward the pickup roller when a maximum number of sheets of paper is loaded into the paper feeding cassette and when only a single sheet of paper is placed in the paper feeding cassette, calculating an amount of consumed paper per one operation of the lifting mechanism as a set value from the calculated difference, lifting the knock-up plate when the paper feeding cassette enters into the printing apparatus until the loaded paper closely contacts the pickup roller, and counting the number of operations of the lifting mechanism, and calculating the amount of paper remaining in the paper feeding cassette based on the number of operations counted and the set value calculated.
The present invention further includes a lifting mechanism for a printer apparatus, for receiving a paper feeding cassette having a knock-up plate on which paper is placed, comprising a rotation shaft installed in said printing apparatus which rotates a lift lever installed at one side thereof, thereby lifting said knock-up plate, a cam gear, driven by a driving source, which connects to said rotation shaft and rotates said rotation shaft a predetermined amount per one turn, and a solenoid which locks said cam gear at each turn by selectively interfering with a locking step formed on said cam gear, wherein the number of operations of said lifting mechanism is calculated by counting the number of operations of said solenoid.